It is known to use propellers to create currents of air in the direction of exchangers to lower the temperature of exothermic engines, such as automotive vehicle engines or other locomotive engines.
In the known manner, a propeller of this type is composed of a central hub, also referred to as the bowl, about which twisted elements commonly referred to as blades are uniformly distributed. The hub is designed to be fitted securely onto the shaft of an engine. The external ends of the blades are generally connected together by an element which is concentric to the hub, commonly referred to as the rim or shell, of which the function is to provide good structural rigidity to the propeller assembly and to ensure the relative support of the different blades. Examples of said propellers, for example, will be found in the patent application WO-2007/107489 A1, which proposes a novel blade profile in order to improve the aeraulic and acoustic performances thereof.
In practice, said propellers have a solid, one-piece structure made of polymer material, which may be reinforced, and are manufactured by an injection-molding method. Said method consists, in simplified form, in injecting the polymer material in the viscous state into a mold, generally via one or more injection-molding ports located in the region of the hub, the material filling the mold flowing into the mold from the area of the mold corresponding to the hub toward the area corresponding to the shell via areas corresponding to the blades. As a result, in the region of the shell, so-called joined-up areas are created where two opposing flows of material, originating from two areas of the mold corresponding to two adjacent blades, meet one another. Said joined-up areas are generally of lower mechanical strength than the remainder of the propeller, as the mixture of the two flows in said areas is never perfectly homogeneous and intimate, due to the differences in temperature between the two front regions of material and the differences in orientation of the fibers of the reinforcing material, in the case where the polymer material is reinforced by a fibrous reinforcement. Said two flows have opposing directions of displacement, and said areas tend to be the collecting point for bubbles of gas or impurities in the interface lines defining said areas, bubbles or impurities which are more difficult to remove via vents in said areas than elsewhere in the mold. In practice, when the propeller ages or is subjected to significant and repeated mechanical stresses, there is an increased risk that it ruptures specifically in the region of one of said joined-up areas of reduced mechanical strength.